improve performance

Hello,

A)
I am going to load a huge amount of data in the DBMS using JDBC 
and I want to reduce as much as possible the required loading time. 

Initially I loaded all data in one transaction. Subsequently, I increased
the number of buffers and disabled fsync() (-o -F) and I loaded the
data again but the performance was almost unchanged. Does it make sense??
How can I improve performance?  To note that no indexes are created on the 
tables and that I load both "insert into" and "create table" statements.
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B)
I want to reduce the space (8 Kb) allocated by 
DBMS when more space is required to load the data in a table. I reduced
the parameter BLCKSZ but the space allocated remains the same, that is 8
KB. 
How can the allocated space be reduced? If the space was reduced  
would loading time and query time increase?

Thank you in advance for your help
Sofia Alexaki